I've been contemplating the question,
"How could someone possibly accomplish effective hypnotic persuasion without the knowledge of the listener?"
and the only way which would make any level of sense at all would require somewhat of a Don Juan; a romantic who, as part of his or her consistent impassioned entourage of abilities, intermixes a pre-devised, well-planned, and extremely well-worded set of instructions into a set of poetry, which is recited nightly in his/her wooing conquest. These words must be delivered just as the lovemaking either is climaxing, or has just climaxed, wherein the target/person is most closely in their subconscious state.
Now, since most guys all but fall asleep after the climax, this is the part where it gets rather impossible, but I could see a woman using this, with grinding, guttural moans and cries, the poetry building an ever more dynamic sexual creshendo, allowing more muse to the soul, as loving wonders escape the lips and tantalize the ears, touching the very heart of the listener while other sensations intertwine to the most arousing orgasm of sight and sound.
Of course, in most cases, a person in an pre-existing relationship would probably never get away with it. The immediate shift in behavior would be suspect.
This would probably only work with someone from the blind of a new date to the death of the acquaintenceship. When one crosses the imaginary line and exaults one's partner out from the crowd, crowning and glorifying that person in other heartfelt emotions, that is when the process actually begins.
The CIA would love this. Set up a standard of objective suggestions to be accomplished each night, watch for signs of response and acting on the suggestions, and then feed more into the subconscious of the target. Each passing day, their seductriss adds more depth to the performance, drawing in their target through this poetic license to kill, leaving open the option to flatly tell the target that it was all staged, giving the ultimate mind-fuck, in just the way writers (like me) would seek our characters to manipulate the anticipation and allure of the audience.
It's a fairly sicko concept, but I believe it can be done.